polymorphism in one to many (WrongClassException)

budi_rostiarso · **Joined:** Thu Dec 22, 2005 7:13 am **Posts:** 1

i create a superclass

Code:

class A{}

and 2 subclass of it

Code:

class AB extends A{}
class AC extends A{}

with mapping of

Code:

  <class polymorphism="implicit" table="a" name="A">
    <id unsaved-value="null" name="id">
      <generator class="native"/>
    </id>
    <discriminator column="type"/>
    <subclass name="AB" discriminator-value="ab"/>
    <subclass name="AC" discriminator-value="ac"/>
  </class>

and i use a collection of AB and AC in other class, namely

Code:

class X
{
private Set ab;
private Set ac;
public Set getAbs(){...}
public Set getAcs(){...}
}

with mapping of

Code:

  <class table="x" name="X">
    <id unsaved-value="null" name="id">
      <generator class="native"/>
    </id>
      <set inverse="true" cascade="save-update" lazy="true" name="abs">
        <key column="id_of_a"/>
        <one-to-many class="AB"/>
      </set>
      <set inverse="true" cascade="save-update" lazy="true" name="acs">
        <key column="id_of_a"/>
        <one-to-many class="AC"/>
      </set>
  </class>

Then i populate the data of ab and ac successfully.
But when i try to call x.getAbs(), it result in a set which consist of both AB and AC
and throw an exception

Code:

org.hibernate.WrongClassException:
Object with id: 36 was not of the specified subclass: AB (loaded object was of wrong class)

It seems that hibernate query for all instance of class A (not spesific for instance of AB), and only filter the query based on the id of X.
What did i do wrong and what do i have to do to get the correct result?

Any help is appreciated.

Thanks.

Hector_Lopez · **Posted:** Fri Dec 23, 2005 5:27 am

From the Hibernate online docs:

"Implicit polymorphism means that instances of the class will be returned by a query that names any superclass or implemented interface or the class and that instances of any subclass of the class will be returned by a query that names the class itself."

http://www.hibernate.org/hib_docs/v3/re ... tion-class

Try using polymorphism="explicit".

Bye.